7
GrAin storAGE GrounD covEr
survEillAncE & monitorinG
tHe Lesser grain borer, a prime pest of stored
grain, is just as likely to be found in native vegetation
and farm paddocks as it is in the grain silos, a new
study into the insect’s behaviour has found.
the unexpected finding poses real challenges
for efforts to control the insect. With increasing
concern about phosphine resistance there was
a need to understand the ecology of these
insects if we are to manage them better.
the ecological research is the first to
establish in any detail where these grain
pests are located outside of grain silos.
this project is focusing on the ecology of the
lesser grain borer (Rhyzopertha dominica) and rust-
red flour beetle (Tribolium castaneum). these pests
were selected for the study as bulk grain handlers
identified these species as the most problematic
in terms of developing resistance to fumigants.
this project is part of the CrC for national
Plant Biosecurity’s Post-Harvest integrity
research Program for the grains industry, which
focuses on insect resistance to phosphine.
the initial trapping of lesser grain borers and
rust-red flour beetles began in september 2008
and concluded in December 2009. traps were
set in southern Queensland between Condamine
and moonie. in southern nsW, Dr mark
stevens, principal research scientist at Yanco
agricultural institute, has collaborated on the
project, setting traps in the Leeton district.
traps were placed adjacent to farm silos,
in cereal paddocks at least one kilometre from
grain silos, or in native vegetation. there were
two additional sites at regional grain depots.
Pheromone traps were set for both insects at all
sites. the traps were put out for one week every four
to six weeks, and the insects caught were sorted and
frozen for further analysis. more than 40,000 lesser
grain borers and 5000 rust-red flour beetles were
trapped during the study, with numbers in individual
traps varying greatly. the greatest number of lesser
grain borers caught in a single trap was 1419, in
nsW, and Queensland recorded the highest number
of rust-red flour beetles in a single trap (387).
trapping shows that these beetles can be found
across the rural landscape. in particular, the lesser
grain borer’s distribution is more widespread than we
initially believed. the borers have been consistently
caught in traps that are significant distances from
grain storages and, in some cases, in greater
storAge Pests BeAt ArounD the Bush
ecology studies have discovered stored grain insects many kilometres from the nearest silos,
raising important questions about survival and their preferred food sources By greg Daglish
As grain insects
have been
found across
the landscape,
the importance
of good hygiene
to reduce the
attraction of grain
storage areas is
important.
trAPPinG
shoWs
thAt thEsE
bEEtlEs
cAn bE
founD
Across
thE rurAl
lAnDscAPE.
numbers compared with traps adjacent to silos.
On one occasion, 887 lesser grain borers were
caught in a single trap in a Queensland national park,
at least five kilometres from the nearest farm. rust-
red flour beetles were concentrated around silos, but
were still caught in traps away from farm storages.
it is not yet clear whether the lesser grain borer
is surviving on unknown host plants or whether they
are travelling long distances to the vegetation sites. if
the findings demonstrate this species is reproducing
and developing on native host plants then a whole
new set of challenges about insect control arise.
However, a more likely explanation is that
beetles are flying great distances from infested
grain and being caught in the traps.
further analysis of the insects preserved from traps
using molecular techniques may help to answer the
question of travel. Population genetics will identify
how closely related insects found around silos are
to those found in paddocks and further afield. a
close genetic relationship in all populations could
indicate insects are travelling much longer distances
than previously thought; a more distant relationship
could indicate that separate populations are surviving
on alternative host plants. results available so far
show a strong relationship between rust-red flour
beetles trapped in the Queensland study area.
there have been differences in the trapping
results between the two states, with nsW traps
catching more insects when they are around, but
for shorter periods. in the two months following
a heatwave in southern nsW in January 2009,
when temperatures reached 40oC or higher for
more than a week, the number of insects of
both species trapped declined dramatically.
in Queensland, warmer than normal temperatures
in late winter coincided with a major increase in
insects trapped, compared with previous months.
these findings suggest weather conditions may
have a significant bearing on insect populations
and further research will investigate these links.
Other aspects of the project include
identifying the levels of phosphine resistance
in different insect populations, although early
results suggest little difference between silo and
paddock-collected lesser grain borers. □
GrDc research code nPb00004 (crcnPb project crc50089)
more information: Dr Greg Daglish, principal research scientist, Department of
employment, economic Development and Innovation, 07 3896 9415;
greg.daglish@deedi.qld.gov.au; www.grdc.com.au/NPB00004